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Purpose: Underwater divers face several potential neurological hazards when breathing compressed gas mixtures including nitrogen narcosis which can impact diver's safety. Various human studies have clearly demonstrated brain impairment due to nitrogen narcosis in divers at 4 ATA using critical flicker fusion frequency (CFFF) as a cortical performance indicator. However, recently some authors have proposed a probable adaptive phenomenon during repetitive exposure to high nitrogen pressure in rats, where they found a reversal effect on dopamine release.Methods: Sixty experienced divers breathing Air, Trimix or Heliox, were studied during an open water dive to a depth of 6 ATA with a square profile testing CFFF measurement before (T0), during the dive upon arriving at the bottom (6 ATA) (T1), 20 min of bottom time (T2), and at 5 m (1.5 ATA) (T3).Results: CFFF results showed a slight increase in alertness and arousal during the deep dive regardless of the gas mixture breathed. The percent change in CFFF values at T1 and T2 differed among the three groups being lower in the air group than in the other groups. All CFFF values returned to basal values 5 min before the final ascent at 5 m (T3), but the Trimix measurements were still slightly better than those at T0.Conclusions: Our results highlight that nitrogen and oxygen alone and in combination can produce neuronal excitability or depression in a dose-related response. [ABSTRACT FROM AUTHOR]

One of the possible risks incurred while diving is inert gas narcosis (IGN), yet its mechanism of action remains a matter of controversy. Although providing insights in the basic mechanisms of IGN, research has been primarily limited to animal studies. A human study, in real diving conditions, was needed. Twenty volunteers within strict biometrical criteria (male, age 30-40 years, BMI 20-23, non smoker) were selected. They performed a no-decompression dive to a depth of 33 mfw for 20 min and were assessed by the means of critical flicker fusion frequency (CFFF) measurement before the dive, during the dive upon arriving at the bottom, 5 min before the ascent, and 30 min after surfacing. After this late measurement, divers breathed oxygen for 15 min and were assessed a final time. Compared to the pre-dive value the mean value of each measurement was significantly different ( p < 0.001). An increase of CFFF to 104 ± 5.1 % upon arriving to the bottom is followed by a decrease to 93.5 ± 4.3 %. This impairment of CFFF persisted 30 min after surfacing, still decreased to 96.3 ± 8.2 % compared to pre-dive CFFF. Post-dive measures made after 15 min of oxygen were not different from control (without nitrogen supersaturation), 124.4 ± 10.8 versus 124.2 ± 3.9 %. This simple study suggests that IGN (at least partially) depends on gas-protein interactions and that the cerebral impairment persists for at least 30 min after surfacing. This could be an important consideration in situations where precise and accurate judgment or actions are essential. [ABSTRACT FROM AUTHOR]

Contribution of skin thermal sensors under inert gas narcosis to the raising hypothermia is not known. Such information is vital for understanding the impact of narcosis on behavioural thermoregulation, diver safety and judgment of thermal (dis)comfort in the hyperbaric environment. So this study aimed at establishing the effects of normoxic concentration of 30% nitrous oxide (NO) on thermo-tactile threshold sensation by studying 16 subjects [eight females and eight males; eight sensitive (S) and eight non-sensitive (NS) to NO]. Their mean (SD) age was 22.1 (1.8) years, weight 72.8 (15.3) kg, height 1.75 (0.10) m and body mass index 23.8 (3.8) kg m. Quantitative thermo-tactile sensory testing was performed on forearm, upper arm and thigh under two experimental conditions: breathing air (air trial) and breathing normoxic mixture of 30% NO (NO trial) in the mixed sequence. Difference in thermo-tactile sensitivity thresholds between two groups of subjects in two experimental conditions was analysed by 3-way mixed-model analysis of covariance. There were no statistically significant differences in thermo-tactile thresholds either between the Air and NO trials, or between S and NS groups, or between females and males, or with respect to body mass index. Some clinically insignificant lowering of thermo-tactile thresholds occurred only for warm thermo-tactile thresholds on upper arm and thigh. The results indicated that normoxic mixture of 30% NO had no influence on thermo-tactile sensation in normothermia. [ABSTRACT FROM AUTHOR]

Previous findings of a narcosis-induced reduction in heat production during cold water immersion, as reflected in oxygen uptake (VO2), have been attributed to the attenuation of the shivering response. The possibility of reduced oxygen utilization (VO2) by the muscles could not, however, be excluded. Accordingly, the present study tested the hypothesis that mild narcosis, induced by inhalation of a normoxic gas mixture containing 30% nitrous oxide (N2O), would affect VO2. Nine male subjects participated in both maximal and submaximal exercise trials, inspiring either room air (AIR) or a normoxic mixture containing 30% N2O. In the submaximal trials, the subjects exercised at 50% of maximal exercise intensity (Wmax) as determined in the maximal AIR trial. Though the subjects attained the same Wmax in the AIR and N2O trials, maximal VO2 was significantly higher (P < 0.05) during the N2O condition [58.9 (SEM 3.1) ml · kg-1 · min-l] compared to the AIR condition [55.0 (SEM 2.4) ml · kg-1 · min-l]. However, the VO2-relative exercise intensity relationship was similar during both maximal AIR and maximal N2O at submaximal exercise intensities. There were no significant differences in the responses of oesophageal temperature, sweating rate, heart rate and ventilation between AIR and N2O in the maximal and submaximal tests. It was concluded that the previously reported narcosis-induced reductions in VO2 observed during cold water immersion can be attributed solely to a reduction in the shivering response rather than to decreased oxygen utilization by the muscles. [ABSTRACT FROM AUTHOR]